The invention relates to a system for transmitting messages, in particular for programming and/or updating electronic devices including memory and/or display components.
The invention also relates to a method for employing such a system.
It applies preferably, but not exclusively, to the updating of data displayed by electronic labels, for example labels displaying a variety of information about a product: price, price per kg, etc. Such labels are arranged on presentation shelves for the aforementioned products in certain sales outlets (supermarkets or the like).
Further to this preferred application in retailing, a system according to the invention can be employed in a variety of other fields: updating timetable displays, etc.
To give a concrete idea, unless otherwise indicated, the preferred area of application of the invention, that is to say the updating of data displayed by electronic labels, will be assumed below.
Such labels are well-known per se. They generally include a memory, means for processing the information, or at least for programming and inputting data in order to record them in the memory, and a display, most often a liquid crystal display in order to save on the energy needed for the device to operate properly. By way of explanation, it is on the one hand beneficial to provide transportable apparatus, and on the other hand the large number of labels customarily used in a sales outlet will in practice prohibit supply by connecting to the mains.
Consideration may be given to programming and/or updating these labels by entering the data manually (for example using a keyboard). This method is time consuming and gives rise to errors.
It has also been proposed to establish computerized links between the labels and a central site for processing information, for example a managing computer. For the reasons indicated above, these links cannot be fixed.
A first class of system according to the prior art employs infrared links. This type of link, entirely comparable with those used in household remote control devices (televisions, etc.) presents the advantage of having a very large bandwidth and can therefore convey signals at a very high rate. However, such links present a major drawback. Specifically, these waves are highly directional and require that the receivers with which the labels are equipped be directed very accurately at the infrared wave emitters, which conflicts with the desired flexibility. It has to be possible to arrange the labels at a number of positions on a shelf, not only along it but also on different levels (racks), which runs the risk of their being placed in xe2x80x9cshadow zonesxe2x80x9d. It is in reality only possible to use this link method for fixed or semifixed installations.
In the prior art, it has also been proposed to use radio waves. However, although this type of link a priori meets the expressed needs, it gives rise to electromagnetic pollution which may prove unacceptable. Further, the standards in this field have been made more stringent: there is in particular an EU regulation in force since January 1996.
While keeping the advantages of the best performing prior art systems, in particular the opportunity for reliably updating a large number of electronic labels in a short time without imposing constraints on the way in which they are arranged, the invention aims to overcome the drawbacks.
To do this, the system according to the invention employs the modulation of visible light, and in particular, in a preferred embodiment, the modulation of light produced by fluorescent tubes.
It has been found that, when the supply frequency of a fluorescent tube is increased, the luminous intensity decreases. The tube behaves as an inductor. The invention profits from this phenomenon.
However, referring for example to the preferred application of the invention, the majority of stores are continuously illuminated with tubes of the aforementioned type. These tubes can therefore be used for the purpose of updating the labels. This will result in minor variations of the background luminosity and pulsations which can be made tolerable by particular arrangements that will be indicated below.
The system according to the invention essentially comprises four parts: a digital encoder, a light modulator which is controlled by the encoder and is used as a transmitter, a receiver sensitive to the modulation of the light emitted by the background illumination components which are controlled by the modulator, and a decoder, associated with signal processing circuits. These last two components constitute the core of the electronic label. It furthermore comprises a display component controlled by the signal processing circuits, the latter conventionally comprising one or more memories (random-access memory, fixed memory, registers). Use will preferably be made of a microcontroller, microprocessor or dedicated circuit, for example of the so-called ASIC type (Application Specific Integrated Circuit) if this is justified by the number of labels made.
According to a first embodiment of the invention, frequency modulation is carried out. Since the encoding is of the binary type, it is sufficient to provide two separate states, as regards modulation, and therefore two frequencies. According to this embodiment, the fluorescent tubes are supplied during the label updating periods by a first frequency to represent a logic xe2x80x9c1xe2x80x9d and a second frequency to represent a logic xe2x80x9c0xe2x80x9d. As indicated above, the emitted luminous intensity decreases with frequency. The luminous intensity received by the electronic labels will therefore fluctuate at the rate of the information sent by the encoder.
According to a preferred embodiment of the invention, pulse width or phase modulation is carried out, around a time interval connected with the period of the supply signals of the fluorescent tubes. Preferably, the reference time interval is chosen equal to the half period of the mains, i.e. 10 ms. Here again, it is sufficient to provide two separate states during the updating phase, which are interpreted by the decoder as a succession of binary states.
The invention therefore relates to a message transmission system comprising a transmitter and at least one receiver, the transmitter comprising a generator of digital data representing the message, means for encoding these data in a determined serial digital code and means for modulating electromagnetic radiation in a determined way, each receiver comprising at least means which are sensitive to said modulated electromagnetic radiation and convert it into electrical signals, and decoding means for reconstructing said message from the converted signals, characterized in that the modulation means control components for illumination with visible light in such a way as to modify the intensity of the emitted light energy in two separate states during the periods in which said messages are sent, in that said means sensitive to the electromagnetic radiation detect these states so as to deliver electrical signals having two separate states.
The invention also relates to a method for employing such a system.
The invention lastly relates to the application of this system to the updating of data displayed by electronic labels arranged on display shelves for articles in a store.